I see this happening much more than it did a few months ago but it now seems to take about 3 seconds after picking up the handset before we can hear each other. Since I get lots of junk calls, I typically hang up only to have the caller try again, which is kind of annoying. So what's up with the delay?

Is the delay only at the beginning when you pick up? If so, is your Vonage device NAT'd behind another router or is your modem also a router?

The number one cause for the 2 - 3 second delay at the beginning of a call is due to RTP packets not coming through the NAT. The way this works is that until your device sends the first RTP packet to the media relay, the media relay wont send any packets to you. With some routers, even though you have sent the first packet out which should open the NAT pinhole and allow the packets from the media relay through the router to your device, it doesn't. So while the media relay is streaming RTP packets to your IP address, your router is treating these packets as DOS and until your device has sent so many packets out, it does not let them in. In some cases, it doesn't let them in therefore 1 way audio. In other cases, it takes so many packets out before it let's them in.

I am not 100% sure you fully understood what I am talking about. QOS will have nothing to do with this. QOS only prioritizes LAN traffic out to the internet. I had mentioned DOS(Denial of Service) in my previous e-mail which you may have misunderstood.

The way NAT works is you send a request from a PC behind the router to the internet. When this packet leaves the router, it is masked with the public IP. The router has a table that knows where to route the packet back one it comes back through the pinhole.

The Vonage media relay will not stream any RTP(audio) packets to your IP until it receives the first packet from you. Assuming there is no hesitation or delay from your Vonage adapter out through your modem sending these RTP packets, what could be happening is your router is restricting the packets back from the media relay thinking it is some sort of DOS attack. The router is closing the NAT pinhole for the session and after you have sent so many packets to the media relay IP, it finally opens this pinhole to let the packets in.

This is why I suggested trying the DMZ. Not sure it will do the trick. Factory resetting your router might do it if the problem only recently started to occur. Make sure that you haven't made any changes to your router or network such as firmware updates. Any such change prior to the issue starting could be a factor.

Last resort to confirm whether or not the router is causing the problem, connect the Vonage adapter directly to the modem and run some test calls.